1. Field of the Invention
The present invention relates to a seat lifter (or seat height adjuster) for adjustment in height of an automotive seat and a lever drive mechanism provided in the seat lifter, which is driven by an operation lever for actuation of the seat lifter for the height adjustment of seat. Particularly, the invention is directed to a seat lifter having forward and rearward links movable interlockingly for adjustment in height of the seat and also to a ratchet-type lever mechanism adaptable for use in the seat lifter to cause such interlocking movement of those two links.
2. Description of Prior Art
A seat height adjuster or what is known as a seat lifter is incorporated in automotive seat to enable an occupant on the seat to selectively adjust the height of seat according to his or her physique and seating posture. In the seat lifter, typically known is a linkage-type seat lifter having forward and rearward links which are interlockingly movable and pivotally coupled with the forward and rearward portions of the seat, respectively, so that the seat may be raised and lowered via those two links. This seat lifter includes plural transmission gears (reduction gears and the like), a brake unit, and a drive mechanism provided with a lever or handle, wherein the drive mechanism is operatively connected through the transmission gears and bake unit to the forward and rearward links. Thus, the drive mechanism is operable by a user who handles its lever to cause both of the two links to move in synchronized way, thereby selectively raising and lowering the seat to a desired point of level.
In this construction of seat lifter, a load is directly transmitted to the drive mechanism via the foregoing constituent elements, and therefore, a much force is required on the user""s part to operate the lever or handle. This poses an unfavorable bar to a smooth and easy operation.
Conventionally, to avoid such defective aspect, a ratchet-type lever mechanism has been employed, which utilizes a known ratchet gear comprising a ratchet gear and ratchet pawl so as to limit the rotation of a lever to one operative direction. With this mechanism, one can simply rotate an operation lever repeatedly in vertical direction, with a small force, due to the combination of ratchet and lever, so that a rotational force is smoothly transmitted to the seat lifter for adjustable vertical movement of the seat to a desired level.
In ordinary, such known ratchet-type lever mechanism requires switching over the direction of rotation of the ratchet gears through operation of secondary associated lever or button. This secondary lever or button is normally disposed adjacent to the main operation lever of the lever mechanism. In most instances, however, the main operation lever of this kind is situated in a narrow space between the lateral side of seat cushion and the door or wall of automobile, which results in a user having to grope for that secondary lever or button to switch over the ratchet gears. Most possibly, this will be a issue of poor usability of the mechanism in that it frequently forces a user to feel for the secondary lever without ascertaining it with his or her own eyes, with the result that the user will erroneously switch over the secondary lever to a wrong operative position. It is therefore of a high likelihood that the user has not noticed this error until he or she handles the main operation lever and then needs to again switch over the secondary lever to a right operative position, which raises a troublesome aspect or a poor usability as well. Further, the provision of such secondary switch-over lever or button leads inevitably to a complicated structure of the ratchet-type lever mechanism on the whole.
Also, with regard to the conventional structure of seat lifter itself, the forward and rearward links thereof are connected, via transmission gears (reduction gears), to the ratchet-type lever mechanism. The gears are prone to wabbling or rattling due to clearances among the gears, and there is the likelihood that the stability or seating touch of seat will be degraded.
In view of the above-stated drawbacks, it is a primary purpose of the present invention to provide an improved seat lifter with ratchet-type lever mechanism which is easy to operate and simplified in structure.
In order to achieve such purpose, the seat lifter of this kind in accordance with the present invention is basically comprised of:
a linkage means for operative connection with the vehicle seat, the linkage means including a first link means and a second link means, each being to be pivotally connected with forward and rearward sides of the vehicle seat, respectively, such as to allow rotative vertical motion of the linkage means, wherein one of said first and second link means is formed with a bell crank portion in an integral manner;
a drive means operatively connected with the linkage means;
the linkage means including a rotation transmission link means operatively connected between those linkage and drive means such that an operative rotation force applied from the drive means is transformed into the rotative vertical motion of the linkage means;
a brake means for providing a braking action to the rotative vertical motion of linkage means;
the rotation transmission link means including a sector gear means which is in a meshed engagement with the brake means; and
the drive means comprising a ratchet-type lever mechanism which includes:
a support base means;
a ratchet gear wheel means having a bearing shaft as the center of rotation thereof, the bearing shaft being rotatably supported by said support base means and securely connected with the brake means;
the ratchet gear wheel means including at least a first ratchet gear wheel and a second ratchet gear wheel, wherein each of the first and second ratchet gear wheel has one-way clutch means built therein, with such an arrangement that the first ratchet gear wheel is to be locked to the shaft in a normal direction for integral rotation therewith, while being allowed to rotate about the shaft in a reverse direction, and that the second ratchet gear wheel is to be locked to the shaft in the reverse direction, while being allowed to rotate about said shaft in the normal direction;
and
a ratchet pawl means rotatably supported by the support base means, the ratchet pawl means including a pair of first and second toothed ratchet pawls which are disposed thereon in correspondence with the respective first and second ratchet gear wheels and further spaced apart from each other by a central angle relative to the center of rotation associated with the shaft of the ratchet gear wheel means; a lever means operatively connected with the ratchet pawl means;
wherein operation of the lever means causes selective rotation of the ratchet pawl means in a selected one of the normal and reverse directions from a neutral position where the ratchet pawl means is normally out of meshed engagement with the ratchet gear wheel means, so that a selected one of the first and second toothed ratchet pawls is rotated in the selected one of normal and reverse directions and brought to meshed engagement with a mating one of the first and second ratchet gear wheels;
and
a biasing means for normally biasing the ratchet pawl means in a direction to the neutral position, thereby normally placing both first and second toothed ratchet pawls in a point out of engagement with the first and second ratchet wheels.
Accordingly, by initially rotating the lever means in a selected one of tow directions, a selected one of the first and second toothed ratchet pawls is brought to meshed engagement with a mating one of the first and second ratchet gear wheels, so that a user can readily select a desired corresponding direction for operation of the drive means of ratchet-type lever mechanism, without any switch-over operation, and then, by continuing to rotate the lever means, the linkage is moved in a selected one of upward and downward directions, thereby allowing the user to adjust the height of seat. Further, the seat lifter per se is Simplified in structure since the linkage means may be basically formed only by the first and second link means and the rotation transmission link means without requiring no other transmission gear mechanism, so that the seat lifter can be easily assembled with a less amount of parts and fittings required.
Another various advantages and features of the present invention will become apparent from reading of the descriptions hereinafter, with reference to the annexed drawings.